Heat sink



FIG. 1 is a perspective view of the heat sink embodying the new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a front elevational view thereof; and,

FIG. 5 is a right side elevational view thereof, the left side being a mirror image thereof.

The bottom of the heat sink forms no part of the claimed design. The broken line showing of supports in FIGS. 3-5 is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for heat sink, as shown and described. 